Redundant circuits are usually concomitantly integrated in integrated circuits in order to be able to activate these as required. Such redundant circuits are activated if individual circuit parts are not functional on account of a defective processing (e.g., defects, particles). The redundant circuits then undertake the task of the defective circuits and the overall chip is fully functional.
In order to activate the redundant circuit, the integrated circuit has to be electrically isolated from the defective region and be connected to a redundant circuit (replacement circuit). This is done by means of fuses for isolating current paths and antifuses for connecting current paths.
An example of a fuse and an antifuse and also a method for production and activation of a fuse and an antifuse emerge from German patent application 196 04 776 A1 and corresponding PCT application WO 97/29515.
These fuses have hitherto been integrated in the metallization layers of the integrated circuit. In order to isolate a fuse, then, a laser beam is directed onto it and the fuse is blown. What is problematic in this case is that the fuse is encapsulated in a dielectric, so that the encapsulating dielectric layer often bursts open during the fuse blowing operation. This then results in reliability problems such as leakage currents, corrosion, etc.
After the processing of the chips has finished, the chips are electrically checked for functionality prior to mounting into a housing. Non-functioning chips are repaired with the fuses as above before they are mounted into housings.